forked from enlightenment/efl
Remove out-dated info about Eet format
SVN revision: 60528
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Iván Briano
parent
f175c06b0c
commit
52511e4cfa
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@ -68,88 +68,6 @@ of Eet, but it serves to illustrate its simplicity.
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@include eet-basic.c
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@section format What does an Eet file look like?
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The file format is very simple. There is a directory block at the start of
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the file listing entries and offsets into the file where they are stored,
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their sizes, compression flags etc. followed by all the entry data strung one
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element after the other.
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All Eet files start with t a 4 byte magic number. It is written using network
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byte-order (big endian, or from most significant byte first to least
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significant byte last) and is 0x1ee7ff00 (or byte by byte 0:1e 1:e7 2:ff
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3:00). The next 4 bytes are an integer (in big endian notation) indicating
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how many entries are stored in the Eet file. 0 indicates it is empty. This is
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a signed integer and thus values less than 0 are invalid, limiting the number
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of entries in an Eet file to 0x7fffffff entries at most. The next 4 bytes is
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the size of the directory table, in bytes, encoded in big-endian format. This
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is a signed integer and cannot be less than 0.
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The directory table for the file follows immediately, with a continuous list
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of all entries in the Eet file, their offset in the file etc. The order of
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these entries is not important, but convention would have them be from first
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to last entry in the file. Each directory entry consiste of 5 integers, one
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after the other, each stored as a signed, big endian integer. The first is
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the offset in the file that the data for this entry is stored at (based from
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the very start of the file, not relative to the end of the directory block).
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The second integer holds flags for the entry. currently only the least
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significant bit (bit 0) holds any useful information, and it is set to 1 if
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the entry is compressed using zlib compression calls, or 0 if it is not
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compressed. The next integer is the size of the entry in bytes stored in the
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file. The next integer is the size of the data when decompressed (if it was
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compressed) in bytes. This may be the same as the previous integer if the
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entry was not compressed. The final integer is the number of bytes used by
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the string identifier for the entry, without the NUL byte terminator, which
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is not stored. The next series of bytes is the string name of the entry, with
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the number of bytes being the same as specified in the last integer above.
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This list of entries continues until there are no more entries left to list.
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To read an entry from an Eet file, simply find the appropriate entry in the
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directory table, find it's offset and size, and read it into memory. If it is
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compressed, decompress it using zlib and then use that data.
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Here is a data map of an Eet file. All integers are encoded using big-endian
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notation (most significant byte first) and are signed. There is no alignment
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of data, so all data types follow immediately on, one after the other. All
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compressed data is compressed using the zlib compress2() function, and
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decompressed using the zlib uncompress() function. Please see zlib
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documentation for more information as to the encoding of compressed data.
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@verbatim
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HEADER:
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[INT] Magic number (0x1ee7ff00)
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[INT] Number of entries in the directory table
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[INT] The size of the directory table, in bytes
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DIRECTORY TABLE ENTRIES (as many as specified in the header):
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[INT] Offest from file start at which entry is stored (in bytes)
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[INT] Entry flags (1 = compressed, 0 = not compressed)
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[INT] Size of data chunk in file (in bytes)
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[INT] Size of the data chunk once decompressed (or the same as above, if not)
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[INT] The length of the string itendifier, in bytes, without NUL terminator
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[STR] Series of bytes for the string identifier, no NUL terminator
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... more directory entries
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DATA STORED, ONE AFTER ANOTHER:
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[DAT] DATA ENTRY 1...
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[DAT] DATA ENTRY 2...
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[DAT] DATA ENTRY 3...
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... more data chunks
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@endverbatim
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The contents of each entry in an Eet file has no defined format as such. It
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is an opaque chunk of data, that is up to the application to deocde, unless
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it is an image, ecoded by Eet, or a data structure encoded by Eet. The data
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itself for these entries can be encoded and decoded by Eet with extra helper
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functions in Eet. eet_data_image_read() and eet_data_image_write() are used
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to handle reading and writing image data from a known Eet file entry name.
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eet_data_read() and eet_data_write() are used to decode and encode program
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data structures from an Eet file, making the loading and saving of program
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information stored in data structures a simple 1 function call process.
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Please see src/lib/eet_data.c for information on the format of these
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specially encoded data entries in an Eet file (for now).
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@section compiling How to compile using Eet ?
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Eet is a library your application links to. The procedure for this is very
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